Your biceps look great; no need to do anything differently with them. (In fact, I suspect they've been doing the bulk of the work on your lat exercises.)
The fact that you 'suck' at flexing/spreading your lats tells me you have a poor mind-muscle connection (MMC) with them. In my experience, MMC with the lats does not come naturally for most people--you have to work at it, to actively create it.
To facilitate lat MMC, consider starting your lat workout with single-arm work designed specifically for this purpose. Use a machine if possible (I prefer the Hammer Strength High Row). Use a really light weight--something you can get 20-30 times without difficulty. Limit your ROM to the fully-flexed portion (ie, your hand will be at your side the whole time). This next part is the key--take your free hand and put it on your working lat, and keep it there as you do the movement. The purpose of this is to physically feel the lat contract. (Don't just palpate the upper aspect near your armpit; do some reps with your hand farther down the 'wing' of your lats.) As you proceed through a set, make slight adjustments to your posture, shoulder height, hip angle, etc, until you find the position that allows you to maximally contract your lat. Use your free hand as a guide to tell you when the lat is flexing hard. And once you're positioned so that your lat is contracting maximally, transfer your mental focus from your free hand to the lat itself--that is, go from feeling the lat contract from the outside to feeling it contract from the inside.
So basically, your using your free hand as a guide to help your brain 'find' your lats.
(Remember, don't worry about the weight--the whole point of the movement is to find your lats.)
Do three sets or so with each arm before moving on. Then, for the rest of your lat workout, do your best to carry that feeling forward--that is, use your newfound MMC to put your work-sets into your lats. Don't be surprised if doing so necessitates dropping your working weights, perhaps substantially. This is very common--almost expected. So if necessary (and it likely will be) check your ego at the gym door, drop the weight, and make your lats do the work.